1. Technical Field
The present invention relates to a technology to detect all or part of an object such as a person or a physical object in an image frame to be shot.
2. Background Art
As a conventional technology, there are technologies for detecting an object (e.g. a person, an animal, and a physical object) or a characteristic part (e.g. a face, and an upper body) of the object in the image frame to be shot. As one example of the conventional technologies, there is a technology for detecting a human face in an image frame to be shot by a digital still camera (hereinafter, referred to as “digital camera”),i.e., a face detection technology. The face detection is processing to judge whether or not a face appears in an arbitrary image frame by searching within the arbitrary image frame through certain processing. Such digital camera controls AE (Automatic Exposure)/AF (Automatic Focus) in accordance with a detected face.
Patent documents 1 and 2 disclose an image processing device and a method for detecting a face.
For example, Patent document 1 discloses a method and an image processing device for discriminating a face from an object other than the face (hereinafter, referred to as “non-face”). Characteristic patterns of elements constituting a face (e.g. an eye, a nose, a mouth, and a chin) are preliminarily learned by using samples of a plurality of human faces (sample object), and the discrimination is performed by using element characteristic information composed of a plurality of parameter values which is learned as described above.
A discriminator disclosed in Patent document 1 stores the element characteristic information for each element constituting a face of the sample object in association with a placement position of each element regarding a standard object who has a face in which each element is standardly placed. Also, a plurality of characteristics that each element constituting a face can have are associated with parameter values which are differ from each other and are included in the element characteristic information for each element.
FIG. 22A shows the image processing device disclosed in Patent document 1. In the image processing device, an image cutout unit 33 cuts out, from an input image frame, an image used for judging whether or not a face appears (hereinafter, “judgment image”). As shown in FIG. 22B, the judgment image is cut out by scanning an image frame to be shot, gradually moving a frame 35 of appropriate pixels (e.g. 1 pixel) from the top left to the bottom right of the image frame to be shot in a direction from left to right or from top to bottom.
The image processing device extracts, from the cutout judgment image, a partial image based on a standard placement position of each element, and judges whether or not a face appears in the judgment image with use of (i) the element characteristic information for an element whose position corresponds to the placement position of the partial image and (ii) characteristics of the extracted partial image.    Patent document 1: U.S. Pat. No. 7,099,510, Specification    Patent document 2: Japanese Patent Application publication No. 2004-62565